transport in plants

Question 1

explain three needs for plant transport systems

Answer 1

METABOLIC DEMANDS- plants need oxygen and glucose transported to them and waste products removed
SIZE- some plants are very small and grow, this means plants need very effective transport systems to move substances both up and down from the tip of the roots
SURFACE AREA : VOLUME RATIO - stems roots and trunk have a small SA:V this means they cannot rely on diffusion to supply their cells with everything they need

Question 2

explain transport systems in dicotyledonous plants

Answer 2

they have a special VASCULAR BUNDLE
which is made of xylem and phloem
herbaceous dicots - soft tissues with a short life cycle
woody dicots - have hard lignified tissues with a long life cycle

Question 3

what is the structure of xylem

Answer 3

made of several cells which are dead
long hollow tubes structures
thick walled xylem parenchyma packs around storing food
containing tannin deposits
has lignified secondary walls providing extra mechanical strength

Question 4

what is the purpose of tannin in plants/xylem

Answer 4

tannin is bitter, and has a astringent-tasting chemical that protects plant tissues from herbivores

Question 5

what is the function of xylem

Answer 5

responsible for transport of water and minerals throughout plants

Question 6

what is the structure of phloem

Answer 6

living tissue

the walls of phloem become perforated to from sieve plates

Question 7

what is the function of phloem

Answer 7

transports food in the form of organic solutes around the plant from the leaves where they are made by photosynthesis
supplies sugars and amino acids for cellular respiration

Question 8

give 4 ways plants need water in metabolism

Answer 8

• turgor pressure gives cell expansion
• photosynthesis
• mineral ions transported
• loss of water by evaporation

Question 9

how are root hair cells adapted as exchange surfaces

Answer 9

• microscopic size means they can penetrate easily between soil particles
• each microscopic hair has a large SA:V ratio
• each hair has a thin surface layer

Question 10

what are the two pathways water moves across a root

Answer 10

• symplast pathway - through cytoplasm connected through a plasmodesmata
• apoplast pathway - through cell wall and the intercellular spaces

Question 11

describe and explain the movement of water into the xylem

Answer 11

• when the water reaches the endodermis of the root the pathway is blocked
• the endodermis has a water proof impenetrable layer called the casparian strip
• this is because of the waxy material called suberin in the walls of the endodermis
• in order to cross the endodermis, the water that has been moving via apoplast should now be moving via symplast pathway through the cell surface membrane and into the cytoplasm
• this is important as toxic solutes can be removed from the soil allowing water to enter

Question 12

explain the difference between transpiration and the transpiration stream?

Answer 12

• transpiration is the evaporation from the surface of a leaf
• transpiration stream is the flow of water moved up from soil into root hair through root cortex by osmosis into xylem and up through stem by cohesion of water molecules.

Question 13

describe and explain transpiration

Answer 13

• Transpiration describes the movement and loss of water from plants
• Water enters the leaves and passes into the mesophyll cells by osmosis
• Water evaporates from the leaves to form water vapour – this is important to remember
• Large ‘air spaces’ between the mesophyll cells allow water vapour to collect and diffuse through the leaves
  As a result of this water collecting the water potential rises